Mechanisms for coupling a driving shaft with rotatable elements to be driven are commonly known and exist in many forms. One large group of such coupling elements comprises mechanical clutches and of the field of clutches, one known configuration includes the use of a helical spring having one end secured to either the driving or driven element and the other end free and disposed about the other element to which the first is to be selectively coupled. Frictional engagement of the free end of the spring, typically in the direction in which the end of the helical spring is pointing, with a relatively rotatable one of the elements tends to carry that end with the element about which it is wrapped with the consequence that the helical spring tends to be wrapped tighter causing a decrease in its diameter which in turn tends to shrink the same into engagement with the rotary element about which it is wrapped to tightly grasp the same and transmit rotary motion. In some cases, the same effect may be achieved by causing radial expansion of the spring to engage a radially outer element within which the spring is disposed. In general terms, U.S. Pat. No. 4,440,280, issued on Apr. 3, 1984 to Hagihara is illustrative of such a device in a variety of forms.
Most frequently, clutches of this type are utilized as one way clutches That is, such clutches are utilized to transmit rotary motion to the driven member upon one direction of rotation of the driving member but not the other. Because of this type of usage, they have not been employed to any great degree in variable ratio transmission system where a certain attribute of such clutches could be highly advantageous. For example, clutches of this sort engage with a minimum of shock loading which in turn minimizes the fatiguing of various components of a clutch mechanism.
The present invention is, therefore, directed to providing a unique spring clutch mechanism that may be advantageously employed in variable ratio transmissions to take advantage of the low shock loading that occurs during engagement of such clutches and which may be readily controlled in terms of engagement and disengagement so as to allow disengagement for either direction of rotation of the driving shaft.